The GRP received the phone call from an unidentified person, they said.
In view of the 'bomb threat' and Haryana Teacher's Eligibility test today and tomorrow, and the upcoming Chatt festival, security was tightened at all stations of Ambala Division of Northern Railway, GRP in-charge Raj Kumar said.
A joint team of GRP and Railway Protection Force personnel conducted a day-long search operation at Sonepat station while a Bomb Detection Squad was stationed there as a precautionary measure, he said.